Surprising even the study’s authors, the impact of soot is twice as large as prior assessments, co-author Sarah Doherty of the Joint Institute for the Study of the Atmosphere and Ocean told BBC News, making soot—also called black carbon—the second largest manmade contributor to global warming after carbon dioxide. “If we did everything, we could to reduce these emissions,” co-author Piers Forster of the University of Leeds in the United Kingdom said in a statement. “We could buy ourselves up to half a degree (Celsius) less warming—or a couple of decades of respite.”

Soot emissions have been decreasing in Europe and North America in recent years due to stricter regulations on diesel engines. However, they have been steadily increasing in developing countries. “This study suggests we should be putting even more effort into reducing black carbon pollution,” Durwood Zaelke, head of the Institute for Governance and Sustainable Development in Washington, DC, told Nature. “Reducing black carbon gives you immediate cooling.”

Last year, six countries initiated an effort to reduce climate change agents such as black carbon, including Bangladesh, Canada, Ghana, Mexico, Sweden, and the United States. Their goal is to treat the mitigation of these pollutants as a collective challenge, according to their website. However, the authors of the study warn that while cutting back on soot may help, reducing carbon dioxide emissions is still the best way to address global warming in the long run, according to BBC News.

<blockquote>When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all black-carbon- rich sources becomes slightly negative (-0.06 W m-2 with 90% uncertainty bounds of -1.45 to +1.29 W m-2).</blockquote>

Here is another comment from the same web page:

Stop right there. Second? What about water vapor? Isn’t that nice how they just ignore the elephant in the living room? Sigh. Wake me when the scientific method makes a come back!

blast from the past:
Science 9 July 1971:
Vol. 173 no. 3992 pp. 138-141
Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate
S. I. Rasool, S. H. Schneider
Abstract
Effects on the global temperature of large increases in carbon dioxide and aerosol densities in the atmosphere of Earth have been computed. It is found that, although the addition of carbon dioxide in the atmosphere does increase the surface temperature, the rate of temperature increase diminishes with increasing carbon dioxide in the atmosphere. For aerosols, however, the net effect of increase in density is to reduce the surface temperature of Earth. Because of the exponential dependence of the backscattering, the rate of temperature decrease is augmented with increasing aerosol content. An increase by only a factor of 4 in global aerosol background concentration may be sufficient to reduce the surface temperature by as much as 3.5 ° K. If sustained over a period of several years, such a temperature decrease over the whole globe is believed to be sufficient to trigger an ice age.